I think alchemy/herbalism is a good moneymaker, it kept me in the latest gear all the way to 60 with my priest, with enough left over for training and mount. I have an absurd amount of gold sitting around now, from selling Arcanite Bars and potions, but the herbs themselves sell for more than the potion in most cases. Getting the herbs isn't a problem, and all but the lowest level ones like Peacebloom sell well at AH. You can make a living just selling Swiftthistle to rogues for Thistle Tea and it's an easy herb to find at lower levels.
I'm experimenting with other characters and mining does bring in the silver, too, and so does Enchanting. Disenchanting greens I get from questing or from my other characters is really profitable, once you begin to get shards from the items. On my server, skinning is the least profitable trade, possibly because there are just a lot of skinners out there. That's odd since many other trades use skins of one kind or another.
If you're not into RP then take two gathering professions until you get closer to 60, then switch to a crafting trade like Alchemy or Blacksmithing. I don't think you can make a lot with Engineering since most of what you make can only be used by other engineers, but I haven't tried it at higher levels yet. If you take two gathering trades, I'd make skinning your second one, so you won't need to switch back and forth between detecting herbs and ore.